<div id="map"></div>

<script>
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v9'
    });

    map.on('styleimagemissing', function(e) {
        var id = e.id; // id of the missing image

        // check if this missing icon is one this function can generate
        var prefix = 'square-rgb-';
        if (id.indexOf(prefix) !== 0) return;

        // extract the color from the id
        var rgb = id
            .replace(prefix, '')
            .split(',')
            .map(Number);

        var width = 64; // The image will be 64 pixels square
        var bytesPerPixel = 4; // Each pixel is represented by 4 bytes: red, green, blue, and alpha.
        var data = new Uint8Array(width * width * bytesPerPixel);

        for (var x = 0; x < width; x++) {
            for (var y = 0; y < width; y++) {
                var offset = (y * width + x) * bytesPerPixel;
                data[offset + 0] = rgb[0]; // red
                data[offset + 1] = rgb[1]; // green
                data[offset + 2] = rgb[2]; // blue
                data[offset + 3] = 255; // alpha
            }
        }

        map.addImage(id, { width: width, height: width, data: data });
    });

    map.on('load', function() {
        map.addSource('points', {
            'type': 'geojson',
            'data': {
                'type': 'FeatureCollection',
                'features': [
                    {
                        'type': 'Feature',
                        'geometry': {
                            'type': 'Point',
                            'coordinates': [0, 0]
                        },
                        'properties': {
                            'color': '255,0,0'
                        }
                    },
                    {
                        'type': 'Feature',
                        'geometry': {
                            'type': 'Point',
                            'coordinates': [50, 0]
                        },
                        'properties': {
                            'color': '255,209,28'
                        }
                    },
                    {
                        'type': 'Feature',
                        'geometry': {
                            'type': 'Point',
                            'coordinates': [-50, 0]
                        },
                        'properties': {
                            'color': '242,127,32'
                        }
                    }
                ]
            }
        });

        map.addLayer({
            'id': 'points',
            'type': 'symbol',
            'source': 'points',
            'layout': {
                'icon-image': ['concat', 'square-rgb-', ['get', 'color']]
            }
        });
    });
</script>
